Endocrinology · PANCE / PANRE

Male Hypogonadism

Failure of testes to produce adequate testosterone, spermatozoa, or both — primary (testicular) or secondary (pituitary/hypothalamic).

Also known as: male hypogonadism, low testosterone, low T, androgen deficiency, testosterone deficiency, hypogonadotropic hypogonadism, Klinefelter syndrome, Kallmann syndrome

Overview

Clinical syndrome resulting from failure of the testes to produce physiologic levels of testosterone (androgen deficiency) and/or normal numbers of spermatozoa due to disruption at one or more levels of the hypothalamic-pituitary-testicular axis. Classified as primary (hypergonadotropic; testicular failure) or secondary (hypogonadotropic; hypothalamic-pituitary disease), with combined forms also occurring.

Epidemiology

Prevalence rises with age and comorbidity. Approximately 2-6% of adult men have symptomatic hypogonadism; prevalence reaches 20-50% in men with obesity, type 2 diabetes, or chronic opioid use. Klinefelter syndrome (47,XXY) is the most common primary hypogonadism, affecting ~1 in 600 live male births.

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Risk factors

Primary: Klinefelter syndrome (47,XXY), cryptorchidism, mumps orchitis, testicular torsion or trauma, chemotherapy (alkylating agents), radiation, hemochromatosis
Secondary: pituitary adenoma, hyperprolactinemia, Kallmann syndrome (with anosmia), hypothalamic infiltrative disease, traumatic brain injury, cranial irradiation
Functional secondary: chronic opioid use, glucocorticoid therapy, obesity (BMI >30), type 2 diabetes, metabolic syndrome, obstructive sleep apnea, chronic systemic illness, anabolic steroid use and withdrawal
Anabolic-androgenic steroid abuse with subsequent hypothalamic-pituitary-testicular suppression

Pathophysiology

Testosterone production by Leydig cells is driven by pulsatile LH from the pituitary, itself stimulated by pulsatile GnRH from the hypothalamus. Sertoli cell function (spermatogenesis, inhibin B secretion) requires FSH and intratesticular testosterone. Disruption at the testes (Leydig and seminiferous tubule failure) elevates LH and FSH (primary hypogonadism). Disruption at the hypothalamus or pituitary lowers LH and FSH despite low testosterone (secondary hypogonadism). Obesity contributes via increased aromatase activity (testosterone → estradiol), increased estrogen-mediated negative feedback, and decreased SHBG.

Clinical presentation

Symptoms

Sexual: reduced libido, erectile dysfunction (especially morning erections), reduced spontaneous erections, infertility
Somatic: fatigue, reduced energy, depressed mood, poor concentration, hot flushes (severe deficiency)
Body composition: loss of muscle mass and strength, increased visceral adipose tissue
Skeletal: low-trauma fractures, height loss from vertebral compression
Hair: decreased frequency of shaving, loss of axillary and pubic hair (chronic)
Congenital secondary hypogonadism: failure of pubertal development, delayed puberty, eunuchoid proportions

Signs / physical exam

Reduced testicular volume (normal >15 mL by Prader orchidometer; <6 mL in Klinefelter)
Soft testes (primary) versus normal-feeling small testes (secondary)
Gynecomastia
Decreased body and facial hair, reduced muscle mass
Eunuchoid proportions (arm span >2 cm greater than height; lower body segment > upper) if hypogonadism predates epiphyseal closure
Anosmia in Kallmann syndrome — test smell directly

Classic findings

Klinefelter syndrome: tall stature, small firm testes (<6 mL), gynecomastia, learning difficulties, infertility — karyotype 47,XXY confirms.

Differential diagnosis

Depression — Anhedonia, low mood, sleep and appetite changes overlap with hypogonadism; normal testosterone or borderline; mood improves with treatment of depression alone
Hypothyroidism — Fatigue, weight gain, decreased libido; elevated TSH; resolves with thyroid hormone replacement
Anemia of chronic disease — Fatigue and low energy; CBC and iron studies; treat underlying cause
Obstructive sleep apnea — Daytime somnolence, witnessed apneas, obesity; polysomnography; CPAP often normalizes testosterone partially
Polypharmacy / opioid-induced androgen deficiency — Chronic opioid therapy suppresses GnRH and LH; consider opioid taper or rotation before lifelong testosterone replacement
Klinefelter syndrome (specific primary cause) — Small firm testes (<6 mL), tall stature, gynecomastia, learning difficulties; karyotype confirms 47,XXY
Kallmann syndrome (specific secondary cause) — Congenital secondary hypogonadism with anosmia or hyposmia; failure of GnRH neuron migration; small testes, eunuchoid proportions

Diagnostic workup

Diagnostic criteria

Two morning total testosterone values below the laboratory reference range (typically <264 ng/dL) in a man with symptoms or signs consistent with androgen deficiency, plus determination of primary versus secondary form by LH and FSH.

Labs

Total testosterone — collected fasting between 7-10 AM on two separate mornings (testosterone is diurnal and food-affected); confirm low (<264 ng/dL by Endocrine Society 2018 threshold) before further evaluation
If borderline or altered SHBG (obesity, aging, diabetes, hyperthyroidism, liver disease): free testosterone by equilibrium dialysis or calculated free testosterone with SHBG
LH and FSH — high suggests primary, low or inappropriately normal suggests secondary
Prolactin in all secondary cases (rule out prolactinoma)
Iron studies (ferritin, transferrin saturation) — hemochromatosis
Estradiol if gynecomastia or prior to estradiol-modulating therapy
Karyotype if small firm testes and elevated gonadotropins (suspected Klinefelter)
Semen analysis if fertility concerns

Imaging

MRI of the sella with gadolinium for confirmed secondary hypogonadism, severe hypogonadism (testosterone <150 ng/dL), hyperprolactinemia, or any pituitary symptoms
DEXA scan to assess bone mineral density at baseline in chronic hypogonadism

Diagnostic algorithm

Feature	Primary (Hypergonadotropic)	Secondary (Hypogonadotropic)
Site of defect	Testes	Hypothalamus or pituitary
Testosterone	Low	Low
LH and FSH	Elevated	Low or inappropriately normal
Testicular volume	Often small and firm or normal	Often small and soft
Examples	Klinefelter syndrome, mumps orchitis, chemotherapy, radiation, cryptorchidism, hemochromatosis	Kallmann syndrome, pituitary adenoma, hyperprolactinemia, obesity, opioids, glucocorticoids, anabolic steroid withdrawal
Imaging	Karyotype if Klinefelter suspected	MRI sella with gadolinium
Fertility treatment	Often irreversible; consider ART with retrieved sperm	hCG + FSH, clomiphene, or pulsatile GnRH

Primary versus secondary male hypogonadism — distinguishing features and treatment implications.

Treatment

First-line

Address reversible causes: weight loss in obesity, opioid taper, treat OSA with CPAP, discontinue offending agents (chronic glucocorticoids, anabolic steroids)
Testosterone replacement — testosterone cypionate IM (100-200 mg every 1-2 weeks), testosterone gel (1% or 1.62% applied to upper arms or shoulders daily), intranasal testosterone (Natesto, three times daily), testosterone enanthate IM, transdermal patch, subcutaneous testosterone enanthate auto-injector, or testosterone undecanoate pellets
Treat underlying pituitary or hypothalamic disease (transsphenoidal surgery for macroadenoma, dopamine agonist for prolactinoma)

Second-line / adjunct

Fertility preservation: human chorionic gonadotropin (hCG) with or without recombinant FSH (follitropin alfa, follitropin beta) — preferred over exogenous testosterone if fertility desired, since testosterone suppresses spermatogenesis
SERM (clomiphene citrate, off-label) — for secondary hypogonadism in men who wish to preserve fertility; raises endogenous LH/FSH/testosterone without suppressing spermatogenesis
Aromatase inhibitor — anastrozole — selected obese men with high estradiol and persistent symptoms despite testosterone (limited evidence)
Pulsatile GnRH via pump — congenital hypogonadotropic hypogonadism (Kallmann), particularly for fertility induction

Complications

Osteoporosis and low-trauma fractures
Sarcopenia, frailty, and falls in older men
Infertility
Metabolic syndrome, type 2 diabetes (bidirectional relationship)
Depression and decreased quality of life
Testosterone replacement risks: erythrocytosis (hematocrit >54%), worsening obstructive sleep apnea, acne, fluid retention, suppression of spermatogenesis (paradoxical infertility), gynecomastia from aromatization, possible increased cardiovascular risk in selected high-risk men

PANCE pearls

Never diagnose hypogonadism on a single afternoon testosterone — confirm with two morning (7-10 AM) fasting samples; values fluctuate diurnally and post-prandially.
Testosterone replacement SUPPRESSES spermatogenesis by inhibiting LH and FSH — men of reproductive age who wish to preserve fertility should be treated with hCG (with or without FSH) or clomiphene rather than exogenous testosterone.
Monitor hematocrit (stop or reduce dose if >54%), PSA in men over 40, and lipid panel during testosterone replacement; obtain a baseline DEXA scan.
Klinefelter syndrome is widely under-recognized — consider karyotype in any man with primary hypogonadism, infertility, gynecomastia, or learning difficulty.
Functional secondary hypogonadism (obesity, opioids, OSA, glucocorticoids) often resolves with treatment of the underlying condition — testosterone replacement is not always the answer.

References

Endocrine Society 2018 — Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline (Bhasin et al., J Clin Endocrinol Metab 2018)
AUA 2018 — American Urological Association Guideline on the Evaluation and Management of Testosterone Deficiency (Mulhall et al., J Urol 2018)
AACE 2002 — American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Evaluation and Treatment of Hypogonadism in Adult Male Patients (Petak et al., Endocr Pract 2002)
TRAVERSE Trial — Cardiovascular Safety of Testosterone-Replacement Therapy (Lincoff et al., NEJM 2023)

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